Synthesis of a Crystalline and Transparent Aerogel Composed of Ni-Al Layered Double Hydroxide Nanoparticles through Crystallization from Amorphous Hydrogel.

Enormous efforts have been devoted to the development of crystalline aerogels toward heterogeneous catalysis, energy storage, ion/molecular absorption, and luminescence. However, properties of aerogels are not fully exploited due to their low content of functional moieties embedded in their solid networks, low crystallinity, and limited chemical compositions. Herein, we develop a one-pot approach based on crystallization from amorphous metal hydroxides modified with a ß-diketone ligand, toward crystalline transition-metal hydroxide aerogels. Synthesis of monolithic and crystalline aerogels of layered double hydroxide (LDH) was performed in a Ni-Al system starting from aqueous ethanol solutions of NiCl2·6H2O and AlCl3·6H2O with acetylacetone (acac) as an organic ligand. Propylene oxide (PO) as an alkalization reagent was added into precursory solutions to yield monolithic wet gels. The successive pH increase induces the formation of a three-dimensional (3-D) solid framework composed of amorphous Al(OH)3. Then, amphoteric Al(OH)3 undergoes crystallization into Ni-Al LDH via an acetylacetone-driven dissolution-crystallization of metal hydroxides without destroying the preformed 3-D solid framework. The process allows us to obtain crystalline aerogel monoliths with high porosity and high transparency after supercritical CO2 drying of wet gels. The present scheme can be expected to synthesize functionalized aerogel composed of crystalline transition-metal oxide/hydroxide nanobuilding blocks (NBBs).

Preparation of Silicophosphate Alternating Hybrid Copolymers via Nonaqueous Acid-Base Reactions of Phosphoric Acid and Organo-Bridged Bis(chlorosilane).

A design of atomic and oligomer level structure in organic-inorganic hybrid materials is highly important for various applications. Nonaqueous acid-base reaction allows us to prepare silicophosphates with controlled inorganic networks (-(O-P-O-Si)n) at atomic level because phosphorous and silicon-based precursors can react directly, resulting in an alternating copolymer network. Organic functionalization in those materials has been realized so far by using organic-modified phosphorous acid and/or organo-chlorosilane as precursors. In the present study, silicophosphate oligomers exhibiting inorganic-organic hybrid chains of (-(O-P-O-Si-R-Si)n) (R: bridging organic functional groups), are prepared from phosphoric acid and organo-bridged bis(chlorosilane). The 1, 2-bis(chlorodimethylsilyl)ethane ((C2H4)(Me2SiCl)2) and 1, 4-bis(chlorodimethylsilyl)benzene ((C6H4)(Me2SiCl)2) were used as organo-bridged bis(chlorosilane). Different types of silicophosphate oligomers with different network structures and terminal groups (P-OH and/or Si-Cl) were prepared by changing the reaction temperature and molar ratio of precursors. The formation of low molecular weight oligomers of ring and cage morphologies (ring tetramer, cage pentamer, and ring hexamer) is suggested in the product prepared from phosphoric acid and (C6H4)(Me2SiCl)2 molecule at 150 °C. Those silicophosphate hybrid oligomers are expected to be used as building blocks of hybrid materials with well-defined network structures for desired functionalities.

MOF-on-MOF: Oriented Growth of Multiple Layered Thin Films of Metal-Organic Frameworks.

The precise alignment of multiple layers of metal-organic framework (MOF) thin films, or MOF-on-MOF films, over macroscopic length scales is presented. The MOF-on-MOF films are fabricated by epitaxially matching the interface. The first MOF layer (Cu2 (BPDC)2 , BPDC=biphenyl-4,4'-dicarboxylate) is grown on an oriented Cu(OH)2 film by a "one-pot" approach. Aligned second (Cu2 (BDC)2 , BDC=benzene 1,4-dicarboxylate, or Cu2 (BPYDC)2 , BPYDC=2,2'-bipyridine-5,5'-dicarboxylate) MOF layers can be deposited using liquid-phase epitaxy. The co-orientation of the MOF films is confirmed by X-ray diffraction. Importantly, our strategy allows for the synthesis of aligned MOF films, for example, Cu2 (BPYDC)2 , that cannot be grown on a Cu(OH)2 surface. We show that aligned MOF films furnished with Ag nanoparticles show a unique anisotropic plasmon resonance. Our MOF-on-MOF approach expands the chemistry of heteroepitaxially oriented MOF films and provides a new toolbox for multifunctional porous coatings.

Centimetre-scale micropore alignment in oriented polycrystalline metal-organic framework films via heteroepitaxial growth.

The fabrication of oriented, crystalline films of metal-organic frameworks (MOFs) is a critical step toward their application to advanced technologies such as optics, microelectronics, microfluidics and sensing. However, the direct synthesis of MOF films with controlled crystalline orientation remains a significant challenge. Here we report a one-step approach, carried out under mild conditions, that exploits heteroepitaxial growth for the rapid fabrication of oriented polycrystalline MOF films on the centimetre scale. Our methodology employs crystalline copper hydroxide as a substrate and yields MOF films with oriented pore channels on scales that primarily depend on the dimensions of the substrate. To demonstrate that an anisotropic crystalline morphology can translate to a functional property, we assembled a centimetre-scale MOF film in the presence of a dye and showed that the optical response could be switched 'ON' or 'OFF' by simply rotating the film.

High-Density Protein Loading on Hierarchically Porous Layered Double Hydroxide Composites with a Rational Mesostructure.

Hierarchically porous biocompatible Mg-Al-Cl-type layered double hydroxide (LDH) composites containing aluminum hydroxide (Alhy) have been prepared using a phase-separation process. The sol-gel synthesis allows for the hierarchical pores of the LDH-Alhy composites to be tuned, leading to a high specific solid surface area per unit volume available for high-molecular-weight protein adsorptions. A linear relationship between the effective surface area, SEFF, and loading capacity of a model protein, bovine serum albumin (BSA), is established following successful control of the structure of the LDH-Alhy composite. The threshold of the mean pore diameter, Dpm, above which BSA is effectively adsorbed on the surface of LDH-Alhy composites, is deduced as 20 nm. In particular, LDH-Alhy composite aerogels obtained via supercritical drying exhibit an extremely high capacity for protein loading (996 mg/g) as a result of a large mean mesopore diameter (>30 nm). The protein loading on LDH-Alhy is >14 times that of a reference LDH material (70 mg/g) prepared via a standard procedure. Importantly, BSA molecules pre-adsorbed on porous composites were successfully released on soaking in ionic solutions (HPO4(2-) and Cl(-) aqueous). The superior capability of the biocompatible LDH materials for loading, encapsulation, and releasing large quantities of proteins was clearly demonstrated.

Synthesis of Hydrophilic Poly(vinylpyrrolidone)/CuS Free-Standing Thin Films Exhibiting Photothermal Conversion.

Free-standing films without the need for any support materials attract attention because of their excellent flexibility in use and ability to be transferred to various substrates. However, free-standing films containing large amounts of inorganic crystalline particles are hard to achieve due to their low strength. In this study, we found the possibility of preparing a free-standing composite film of CuS/polyvinylpyrrolidone (PVP) at a large loading of CuS (>50%) from a concentrated colloidal dispersion of CuS nanoparticles modified with PVP. Despite the large amount of inorganic crystals contained in the free-standing film, the film was strong enough to be handled without any support materials. As a proof-of-concept application of the free-standing film, a solar water evaporation experiment was performed. The CuS/PVP free-standing film exhibited photothermal conversion under light illumination to generate heat and accelerate water evaporation, achieving an evaporation rate of 4.35 kg·m-2 h-1 and an evaporation efficiency of 96.3% at a power density of 3 suns. In addition, thanks to the free-standing feature, one side of the CuS/PVP film could be hydrophobized with polydimethylsiloxane to form a Janus thin film, allowing for floating on the water surface. As a result, effective water evaporation was achieved because of the selective evaporation of water from the air/water interface.

Fusion of phosphole and 1,1'-biacenaphthene: phosphorus(V)-containing extended π-systems with high electron affinity and electron mobility.

A profusion of phospholes: Diacenaphtho[1,2-b:1',2'-d]phospholes, a new class of arene-fused phosphole π-systems, were synthesized and their structural and electrochemical properties studied. The P-sulfide derivative has a high electron-transporting ability (µ(E) =2.4×10(-3) cm(2) V(-1) s(-1)) in a vacuum-deposited film.

Thermo-responsive wettability via surface roughness change on polymer-coated titanate nanorod brushes toward fast and multi-directional droplet transport.

A novel approach for thermo-responsive wettability has been accomplished by surface roughness change induced by thermal expansion of paraffin coated on titanate nanostructures. The surface exhibits thermo-responsive and reversible wettability change in a hydrophobic regime; the surface shows superhydrophobicity with contact angles of ∼157° below 50 °C and ∼118° above 50 °C due to a decrease of surface roughness caused by thermally-expanded paraffin at higher temperatures. Reversible wettability change of ∼40° of a contact angle allows for fast and multi-directional droplet transport. The present approach affords a versatile selection of materials and wide variety of contact angles, promoting both scientific advancement and technology innovation in the field of smart surfaces.

Controlling the alignment of 1D nanochannel arrays in oriented metal-organic framework films for host-guest materials design.

Controlling the direction of molecular-scale pores enables the accommodation of guest molecular-scale species with alignment in the desired direction, allowing for the development of high-performance mechanical, thermal, electronic, photonic and biomedical organic devices (host-guest approach). Regularly ordered 1D nanochannels of metal-organic frameworks (MOFs) have been demonstrated as superior hosts for aligning functional molecules and polymers. However, controlling the orientation of MOF films with 1D nanochannels at commercially relevant scales remains a significant challenge. Here, we report the fabrication of macroscopically oriented films of Cu-based pillar-layered MOFs having regularly ordered 1D nanochannels. The direction of 1D nanochannels is controllable by optimizing the crystal growth process; 1D nanochannels align either perpendicular or parallel to substrates, offering molecular-scale pore arrays for a macroscopic alignment of functional guest molecules in the desired direction. Due to the fundamental interest and widespread technological importance of controlling the alignment of functional molecules and polymers in a particular direction, orientation-controllable MOF films will open up the possibility of realising the potential of MOFs in advanced technologies.

Imparting CO2 reduction selectivity to ZnGa2O4 photocatalysts by crystallization from hetero nano assembly of amorphous-like metal hydroxides.

Imparting an enhanced CO2 reduction selectivity to ZnGa2O4 photocatalysts has been demonstrated by controlled crystallization from interdispersed nanoparticles of zinc and gallium hydroxides. The hydroxide precursor in which Zn(ii) and Ga(iii) are homogeneously interdispersed was prepared through an epoxide-driven sol-gel reaction. ZnGa2O4 obtained by a heat-treatment exhibits a higher surface basicity and an enhanced affinity for CO2 molecules than previously-reported standard ZnGa2O4. The enhanced affinity for CO2 molecules of the resultant ZnGa2O4 leads to highly-selective CO evolution in CO2 photo-reduction with H2O reductants. The present scheme is promising to achieve desirable surface chemistry on metal oxide photocatalysts.

Design of Carbon Dots Photoluminescence through Organo-Functional Silane Grafting for Solid-State Emitting Devices.

Advanced optical applications of fluorescent carbon dots (C-dots) require highly integrated host-guest solid-state materials with a careful design of C-dots - matrix interface to control the optical response. We have developed a new synthesis based on the grafting of an organo-functional silane (3-glycidyloxypropyltrimethoxysilane, GPTMS) on amino-functionalized C-dots, which enables the fabrication of highly fluorescent organosilica-based hybrid organic-inorganic films through sol-gel process. The GPTMS grafting onto C-dots has been achieved via an epoxy-amine reaction under controlled conditions. Besides providing an efficient strategy to embed C-dots into a hybrid solid-state material, the modification of C-dots surface by GPTMS allows tuning their photoluminescence properties and gives rise to an additional, intense emission around 490 nm. Photoluminescence spectra reveal an interaction between C-dots surface and the polymeric chains which are locally formed by GPTMS polymerization. The present method is a step forward to the development of a surface modification technology aimed at controlling C-dots host-guest systems at the nanoscale.

Layered Double Hydroxide Nanoclusters: Aqueous, Concentrated, Stable, and Catalytically Active Colloids toward Green Chemistry.

Increasing attention has been dedicated to the development of nanomaterials rendering green and sustainable processes, which occur in benign aqueous reaction media. Herein, we demonstrate the synthesis of another family of green nanomaterials, layered double hydroxide (LDH) nanoclusters, which are concentrated (98.7 g/L in aqueous solvent), stably dispersed (transparent sol for >2 weeks), and catalytically active colloids of nano LDHs (isotropic shape with the size of 7.8 nm as determined by small-angle X-ray scattering). LDH nanoclusters are available as colloidal building blocks to give access to meso- and macroporous LDH materials. Proof-of-concept applications revealed that the LDH nanocluster works as a solid basic catalyst and is separable from solvents of catalytic reactions, confirming the nature of nanocatalysts. The present work closely investigates the unique physical and chemical features of this colloid, the formation mechanism, and the ability to act as basic nanocatalysts in benign aqueous reaction systems.

Transparent and robust siloxane-based hybrid lamella film as a water vapor barrier coating.

Water vapor barriers are important in various application fields, such as food packaging and sealants in electronic devices. Polymer/clay composites are well-studied water vapor barrier materials, but their transparency and mechanical strength degrade with increasing clay loading. Herein, we demonstrate films with good water vapor barrier properties, high transparency, and mechanical/thermal stability. Water vapor barrier films were prepared by the solution crystallization of siloxane hybrid lamellae. The films consist of highly crystallized organic/inorganic hybrid lamellae, which provide high transparency, hardness, and thermal stability and inhibit the permeation of water vapor. The water permeability of a 6 µm thick hybrid film is comparable to that of a 200 µm thick silicon rubber film.

Combining top-down and bottom-up routes for fabrication of mesoporous titania films containing ceria nanoparticles for free radical scavenging.

Nanocomposite thin films formed by mesoporous titania layers loaded with ceria nanoparticles have been obtained by combining bottom-up self-assembly synthesis of a titania matrix with top-down hard X-ray lithography of nanocrystalline cerium oxide. At first the titania mesopores have been impregnated with the ceria precursor solution and then exposed to hard X-rays, which triggered the formation of crystalline cerium oxides within the pores inducing the in situ growth of nanoparticles with average size of 4 nm. It has been observed that the type of coordinating agent in the solution plays a primary role in the formation of nanoparticles. Different patterns have been also produced through deep X-ray lithography by spatially controlling the nanoparticle growth on the micrometer scale. The radical scavenging role of the nanocomposite films has been tested using as a benchmark the UV photodegradation of rhodamine 6G. After impregnation with a rhodamine 6G solution, samples with and without ceria have shown a remarkably different response upon exposure to UV light. The dye photodegradation on the surface of nanocomposite films appears strongly slowed down because of the antioxidation effect of ceria nanoparticles.

Hierarchical nested wrinkles on silica-polymer hybrid films: stimuli-responsive micro periodic surface architectures.

Stimuli-response on hierarchically-structured surface wrinkles is required for advanced filtration, catalysis and sensing applications. Although conventional processes can form hierarchical surface wrinkles, incorporation of stimuli-responsive features has not been achieved, limiting the potential multi-scale functionality of wrinkles. Here, we demonstrate a novel process that can fabricate stimuli-responsive surface hierarchical structures on silica-polymer hybrid films through precisely controlled UV-polymerization and sol-gel condensation. Starting from uniform hybrid films, UV excitation of the film surface triggers the formation of micrometre-scale wrinkles with dual periodicity. Hierarchical nested wrinkle (NW) structures with controllable periodic lengths at discrete size scales of < 10 µm and > 23 µm show a shape-memory effect with changes in the surrounding humidity. Moreover, the individual responses of wrinkles with different periodicities can be controlled independently. As a proof-of-concept application, we demonstrate that the NW structures are an active size-selective adsorption/release surface for micrometre-sized particles.

Titanate nanofunnel brushes: toward functional interfacial applications.

Titanate nanofunnel brushes were grown on sol-gel derived amorphous TiO(2) thin films, whose shape can be tuned from nanosheets to nanofunnels by changing hydrothermal conditions. A superhydrophobic adhesive surface was achieved by a chemical modification of the brushes.

In situ SAXS observation on metal-salt-derived alumina sol-gel system accompanied by phase separation.

The structure formation process of hierarchically porous alumina gels has been investigated by in situ small angle X-ray scattering (SAXS). The measurement was performed on the sol-gel solution containing aluminum chloride hexahydrate (AlCl(3)·6H(2)O), poly(ethylene oxide) (PEO), and propylene oxide (PO). The temporal divergence of scattering intensity in the low q regime was observed in the early stage of reaction, indicating that the occurrence of spinodal-decomposition-type phase separation. Detailed analysis of the SAXS profiles revealed that phase separation occurs between weakly branched polymerizing aluminum hydroxide (AH) and PEO. Further progress of the condensation reaction forms phase-separated two phases, that is, AH-rich phase and PEO-rich phase with the micrometer-range heterogeneity. The growth and aggregation of primary particles occurs in the phase-separated AH-rich domain, and therefore, the addition of PEO influences on the structure in nanometer regime as well as micrometer regime. The moderate stability of oligomeric species allows homogeneous condensation reaction parallel to phase separation and successful formation of hierarchically porous alumina gel.

Structural characterization of hierarchically porous alumina aerogel and xerogel monoliths.

Detailed nanostructures have been investigated for hierarchically porous alumina aerogels and xerogels prepared from ionic precursors via sol-gel reaction. Starting from AlCl3.-6H2O and poly(ethylene oxide) (PEO) dissolved in a H2O/EtOH mixed solvent, monolithic wet gels were synthesized using propylene oxide (PO) as a gelation initiator. Hierarchically porous alumina xerogels and aerogels were obtained after evaporative drying and supercritical drying, respectively. Macroporous structures are formed as a result of phase separation, while interstices between the secondary particles in the micrometer-sized gel skeletons work as mesoporous structures. Alumina xerogels exhibit considerable shrinkage during the evaporative drying process, resulting in relatively small mesopores (from 5.4 to 6.2 nm) regardless of the starting composition. For shrinkage-free alumina aerogels, on the other hand, the median mesopore size changes from 13.9 to 33.1 nm depending on the starting composition; the increases in PEO content and H2O/EtOH volume ratio both contribute to producing smaller mesopores. Small-angle X-ray scattering (SAXS) analysis reveals that variation of median mesopore size can be ascribed to the change in agglomeration state of primary particles. As PEO content and H2O/EtOH ratio increase, secondary particles become small, which results in relatively small mesopores. The results indicate that the agglomeration state of alumina primary particles is influenced by the presence of weakly interacting phase separation inducers such as PEO.